8 replies to this topic

[Chris1275gt]

Hi
I'm trying to thouroughly understand the HS4 carburettor forgive me if this is a simple, probably obvious question but does the butterfly flap on above carb close the aperture when idling and is the fuel/air mix fed to the engine through the small hole drilled in th lower half of the flap as in pic and does the needle in the piston (the type with the spring under the needle clamping end) have to be dead straight or is it flexible like mine. It's on a 75 1275gt.

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[cal844]

That small hole in the flap pulls in air at idle, the needle should have a collar and small spring at the fixing screw, the collar allows movement to reduce needle wear.

The way that carb is pictured is near enough idle setting, full throttle being the plate at almost 90°.

You also want to make sure that once the carb is assembled that the piston drops smoothly.

Sorry I cant be much more help


Cal

Edited by cal844, 07 December 2019 - 10:35 PM.

[Spider]

It's there to reduce NO_X on the over-run.

 

Solder it up.

[cal844]

It's there to reduce NO_X on the over-run.

Solder it up.

Thanks Chris

[Chris1275gt]

It's there to reduce NO_X on the over-run.
 
Solder it up.

Hi Moke
Forgive my ignorance but what is NOx. Could that hole in the flap be a reason when stopping that my idle speed drops to 4/500revs and sometimes stalls. Fuel mix is fine, no air leaks, fuel fine, needle spot on, piston and dash pot smooth as a bucket full of shxte dash pot filled with su oil.

[DeadSquare]

 

It's there to reduce NO_X on the over-run.
 
Solder it up.

Hi Moke
Forgive my ignorance but what is NOx. Could that hole in the flap be a reason when stopping that my idle speed drops to 4/500revs and sometimes stalls. Fuel mix is fine, no air leaks, fuel fine, needle spot on, piston and dash pot smooth as a bucket full of shxte dash pot filled with su oil.

 

NOx = Nitrous Oxide...................LOX = Liquid Oxygen.................Pox = ...as in chicken pox.

 

If you are worried about the effect of soldering up the hole, try a Gaffer Tape patch and see if there is a difference.

[cal844]

Try turning the fuel up a flat, if no difference return to what you had

[Magneto]

check for wear in the bores for the throttle shaft, that can cause an erratic idle. There are kits available to fix them....

[nicklouse]

some reading https://sucarb.co.uk...ion-adjustments